Method and system to vary suction temperature to postpone frost formation

ABSTRACT

A cooling system includes an evaporator coil and a compressor fluidly coupled to the evaporator coil. A circulation fan is arranged to direct air through the evaporator coil and through a discharge air duct into a conditioned space. At least one sensor is disposed in at least one of the discharge air duct, the conditioned space, and the evaporator coil. An HVAC controller is electrically coupled to the at least one sensor and electrically coupled to the compressor. The HVAC controller is configured to receive a measurement of an HVAC parameter from the at least one sensor, determine if the HVAC parameter indicates frost formation on the evaporator coil, and, responsive to a determination that the HV AC parameter indicates frost formation on the evaporator coil, raise a saturated suction temperature of the evaporator coil.

TECHNICAL FIELD

The present disclosure relates generally to refrigerated display cases and more particularly, but not by way of limitation to refrigerated display cases that vary saturated suction temperature in order to delay frost formation.

BACKGROUND

This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

Display cases that are capable of refrigerating contents are common features in many retail outlets. Refrigerated display cases often include a fan that circulates refrigerated air over contents of the refrigerated display case. Such display cases require periodic defrosting. Frost formation will often occur quickly after completion of a defrost cycle. Frost formation leads to diminished efficiency of an evaporator coil. Additionally, frost formation interferes with an air curtain on the display cases allowing increased infiltration of warmer ambient air and leading to elevated product temperatures.

SUMMARY

Various aspects of the disclosure relate to a cooling system. The cooling system includes an evaporator coil and a compressor fluidly coupled to the evaporator coil. A circulation fan is arranged to direct air through the evaporator coil and through a discharge air duct into a conditioned space. At least one sensor is disposed in at least one of the discharge air duct, the conditioned space, and the evaporator coil. An HVAC controller is electrically coupled to the at least one sensor and electrically coupled to the compressor. The HVAC controller is configured to receive a measurement of an HVAC parameter from the at least one sensor, determine if the HVAC parameter indicates frost formation on the evaporator coil, and, responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, raise a saturated suction temperature of the evaporator coil.

Various aspects of the disclosure relate to a method for operating a refrigerated display case. The method includes measuring, by at least one sensor, an HVAC parameter. An HVAC controller, electrically coupled to the at least one sensor, determines if the HVAC parameter indicates frost formation on an evaporator coil. Responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, by the HVAC controller signals an evaporator pressure regulator (“EPR”) to reduce a flow of refrigerant from an evaporator coil to a compressor thereby raising a saturated suction temperature of the evaporator coil.

Various aspects of the disclosure relate to a method for operating a refrigerated display case. The method includes measuring, by at least one sensor, an HVAC parameter. An HVAC controller, electrically coupled to the at least one sensor, determines if the HVAC parameter indicates frost formation on an evaporator coil. Responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, signaling, by the HVAC controller, a compressor to modulate a speed of the compressor thereby raising a saturated suction temperature of the evaporator coil.

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic diagram of a cooling system according to aspects of the disclosure;

FIG. 2 is a flow diagram illustrating a process for operating a refrigerated display case utilizing the cooling system of FIG. 1;

FIG. 3 is a flow diagram illustrating an alternative process for operating a refrigerated display case utilizing the cooling system of FIG. 1

FIG. 4 is a graph of time versus discharge air temperature utilizing existing display cases;

FIG. 5 is a graph of time versus discharge air temperature utilizing the cooling system of FIG. 1;

FIG. 6 is a diagram of product temperature utilizing existing cooling systems;

FIG. 7 is a diagram of product temperature utilizing the cooling system of FIG. 1; and

FIG. 8 is a graph of discharge air temperature versus time comparing existing cooling systems to the cooling system of FIG. 1.

DETAILED DESCRIPTION

Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

FIG. 1 is a schematic diagram of a cooling system 100. The cooling system 100 includes an evaporator coil 102, a condenser coil 104, a compressor 106, and a metering device 108. During operation, a circulation fan 110 circulates air around the evaporator coil 102. In various embodiments, the compressor 106 is, for example, a single-stage compressor, a multi-stage compressor, a single-speed compressor, or a multi-speed compressor. The circulation fan 110, sometimes referred to as a blower, may, in various embodiments, be configured to operate at different capacities (i.e., variable motor speeds) to circulate air through the cooling system 100, whereby the circulated air is conditioned and supplied to a conditioned space 112. In a typical embodiment, the metering device 108 is, for example, a thermostatic expansion valve or a throttling valve. The evaporator coil 102 is fluidly coupled to the compressor 106 via a suction line 114. The compressor 106 is fluidly coupled to the condenser coil 104 via a discharge line 116. The condenser coil 104 is fluidly coupled to the metering device 108 via a liquid line 118.

Still referring to FIG. 1, during operation, to pressure, low-temperature refrigerant is circulated through the evaporator coil 102. The refrigerant is initially in a liquid/vapor state. In a typical embodiment, the refrigerant is, for example, R-22, R-134a, R-410A, R-744, or any other suitable type of refrigerant as dictated by design requirements. Air from within the conditioned space 112, which is typically warmer than the refrigerant, is circulated around the evaporator coil 102 by the circulation fan 110. In a typical embodiment, the refrigerant begins to boil after absorbing heat from the air and changes state to a low-pressure, low-temperature, super-heated vapor refrigerant. Saturated vapor, saturated liquid, and saturated fluid refer to a thermodynamic state where a liquid and its vapor exist in approximate equilibrium with each other. Super-heated ,fluid and super-heated vapor refer to a thermodynamic state where a vapor is heated above a saturation temperature of the vapor. Sub-cooled fluid and sub-cooled liquid refers to a thermodynamic state where a liquid is cooled below the saturation temperature of the liquid.

The low-pressure, low-temperature, super-heated vapor refrigerant is introduced into the compressor 106 via the suction line 114. in a typical embodiment, the compressor 106 increases the pressure of the low-pressure, low-temperature, super-heated vapor refrigerant and, by operation of the ideal gas law, also increases the temperature of the low-pressure, low-temperature, super-heated vapor refrigerant to form a high-pressure, high-temperature, superheated vapor refrigerant. The high-pressure, high-temperature, superheated vapor refrigerant leaves the compressor 106 via the discharge line 116 and enters the condenser coil 104.

Still referring to FIG. 1, outside air is circulated around the condenser coil 104 by a condenser fan 120. The outside air is typically cooler than the high-pressure, high-temperature, superheated vapor refrigerant present in the condenser coil 104. Thus, heat is transferred from the high-pressure, high-temperature, superheated vapor refrigerant to the outside air. Removal of heat from the high-pressure, high-temperature, superheated vapor refrigerant causes the high-pressure, high-temperature, superheated vapor refrigerant to condense and change from a vapor state to a high-pressure, high-temperature, sub-cooled liquid state. The high-pressure, high-temperature, sub-cooled liquid refrigerant leaves the condenser coil 104 via the liquid line 118 and enters the metering device 108.

In the metering device 108, the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant is abruptly reduced. In various embodiments where the metering device 108 is, for example, a thermostatic expansion valve, the metering device 108 reduces the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant by regulating an amount of refrigerant that travels to the evaporator coil 102. Abrupt reduction of the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant causes sudden, rapid, evaporation of a portion of the high-pressure, high-temperature, sub-cooled liquid refrigerant, commonly known as “flash evaporation.” The flash evaporation lowers the temperature of the resulting liquid/vapor refrigerant mixture to a temperature lower than a temperature of the air in the conditioned space 112. The liquid/vapor refrigerant mixture leaves the metering device 108 and returns to the evaporator coil 102.

Still referring to FIG. 1, an evaporator pressure regulator (“EPR”) 122 is disposed in the suction line 114 between the evaporator coil 102 and the compressor 106. In various embodiments, the EPR 122 is an electronically-actuated valve such as, for example, a solenoid valve; however, in other embodiments, other valve types could be utilized. The EPR 122 is electrically coupled to an HVAC controller 130, via a wired or wireless connection, such that, during operation, the HVAC controller 130 signals the ERR 122 to actuate between an open position and a closed position responsive to a measured HVAC parameter. In various embodiments, actuation of the EPR 122 is not limited to a fully-opened state and a fully-closed state. That is, in various embodiments, the EPR 122 may be actuated to an intermediate position that is between the fully-opened state and the fully-closed state. Closure of the EPR 122 reduces a flow of refrigerant between the evaporator coil 102 and the compressor 106 thereby causing refrigerant pressure within the evaporator coil 102 to rise while causing refrigerant pressure at a suction side 132 of the compressor 106 to fall.

Still referring to FIG. 1, a first temperature sensor 124 is disposed within the evaporator coil 102. In various embodiments, the first temperature sensor 124 may be, for example, a thermocouple, a thermometer, a thermostat, or any other appropriate temperature sensor. The first temperature sensor 124 is electrically coupled to the HVAC controller 130 and measures a refrigerant temperature within the evaporator coil 102 (also known as the “saturated suction temperature”). In other embodiments, however, the first temperature sensor 124 may be disposed on an exterior surface of the evaporator coil 102 thereby using an evaporator coil 102 surface temperature as a proxy measurement for the saturated suction temperature. A second temperature sensor 126 is disposed within the conditioned space 112 and is electrically coupled to the HVAC controller 130. In various embodiments, the second temperature sensor 126 may be, for example, a thermocouple, a thermometer, a thermostat, or any other appropriate temperature sensor. In various embodiments, the second temperature sensor 126 is positioned near a discharge air duct 134 so as to measure discharge air temperature; however, in other embodiments, the second temperature sensor 126 may be positioned at any location within the conditioned space 112 so as to accurately measure discharge air temperature. A flow meter 128 is positioned in the discharge air duct 134 and electrically coupled to the EIVAC controller 130. In various embodiments, the flow meter 128 measures a velocity of air discharged from the discharge air duct 134. In various embodiments, the flow meter 128 could be, for example, a rotor-type flow meter or any other type of flow meter. In various embodiments, only one of the first temperature sensor 124, the second temperature sensor 126, and the flow meter 128 may be utilized in operation. Thus, in various embodiments, any two of the first temperature sensor 124, the second temperature sensor 126, and the flow meter 128 could be omitted. In various embodiments, the first temperature sensor 124, the second temperature sensor 126, and the flow meter 128 are electrically coupled to the HVAC controller 130 via, for example, a wired or a wireless connection.

Still referring to FIG. 1, during operation, the HVAC controller 130 receives measurements of the HVAC parameter. In various embodiments, the HVAC parameter could be at least one of, for example, a saturated suction temperature, measured by the first temperature sensor 124, a discharge air temperature, measured by the second temperature sensor 126, or a discharge air velocity, measured by the flow meter 128. If the HVAC controller 130 detects a change in the HVAC parameter that is indicative of frost formation, the HVAC controller 130 signals the EPR 122 to restrict flow of refrigerant from the evaporator coil 102 to the compressor 106. That is, the HVAC controller 130 signals the EPR 122 to move closer to the fully-closed position. In various embodiments, conditions of the HVAC parameter that could be indicative of frost formation include, for example, a saturated suction temperature measured by the first temperature sensor 124 to be below a pre-determined minimum threshold, an increase in discharge air temperature measured by the second temperature sensor 126, or a decrease in discharge air velocity measured by the flow meter 128. Restriction, by the EPR 122, of refrigerant flow between the evaporator coil 102 and the compressor 106 results in the saturated suction temperature rising and frost formation being delayed.

Still referring to FIG. 1, in other embodiments, the ERR 122 could be omitted. In such an embodiment, the HVAC controller 130 receives measurements of the HVAC parameter. If the HVAC controller 130 detects a change in the HVAC parameter that is indicative of frost formation, the HVAC controller 130 modulates a speed of the compressor 106. In embodiments, where the compressor 106 is a variable-speed compressor, the modulation may include adjusting the speed of the compressor 106 to a value between a maximum-rated speed and a minimum-rated speed. In embodiments where the compressor 106 is a fixed-speed compressor, the modulation may include cycling the compressor 106 between an activated state and a deactivated state. Modulation of the speed of the compressor 106 impacts the saturated suction temperature such that the saturated suction temperature can be lowered by either deactivating the compressor 106 or reducing a speed of the compressor 106.

FIG. 2 is a flow diagram illustrating a process 200 for operating a refrigerated display case utilizing the cooling system 100. The process 200 begins at step 201. At step 202, a defrost cycle is completed. At step 204, the HVAC controller 130 receives a measurement of the HVAC parameter. In various embodiments, the HVAC parameter could he at least one of, for example, a saturated suction temperature, measured by the first temperature sensor 124, a discharge air temperature, measured by the second temperature sensor 126, or a discharge air velocity, measured by the flow meter 128. At step 206, the HVAC controller 130 determines if the HVAC parameter indicates frost formation. In various embodiments, conditions of the HVAC parameter that could be indicative of frost formation include, for example, a saturated suction temperature measured by the first temperature sensor 124 to be below a pre-determined minimum threshold, an increase in discharge air temperature measured by the second temperature sensor 126, or a decrease in discharge air velocity measured by the flow meter 128. If, at step 206, the HVAC controller 130 determines that the HVAC parameter indicates frost formation, the process 200 proceeds to step 208. If, at step 206, the HVAC controller 130 determines that the HVAC parameter does not indicate frost formation, the process 200 returns to step 204. At step 208, responsive to a determination that the HVAC parameter indicates frost formation, the HVAC controller 130 signals the EPR 122 to restrict flow of refrigerant from the evaporator coil 102 to the compressor 106. That is, the HVAC controller 130 signals the EPR 122 to move closer to the fully-closed position. Following step 208, the process 200 returns to step 204.

FIG. 3 is a flow diagram illustrating an alternative process 300 for operating a refrigerated display case utilizing the cooling system 100. The process 300 begins at step 301. At step 302, a defrost cycle is completed. At step 304, the HVAC controller 130 receives a measurement of the HVAC parameter. At step 306, the HVAC controller 130 determines if the HVAC parameter indicates frost formation. In various embodiments, conditions of the HVAC parameter that could be indicative of frost formation include, for example, a saturated suction temperature measured by the first temperature sensor 124 to he below a pre-determined minimum threshold, an increase in discharge air temperature measured by the second temperature sensor 126, or a decrease in discharge air velocity measured by the flow meter 128. If, at step 306, the HVAC controller 130 determines that the HVAC parameter indicates frost formation, the process 300 proceeds to step 308. If, at step 306, the HVAC controller 130 determines that the HVAC parameter does not indicate frost formation, the process 300 returns to step 304. At step 308, responsive to a determination that the HVAC parameter indicates frost formation, the FIVAC controller 130 modulates a speed of the compressor 106. In embodiments, where the compressor 106 is a variable-speed compressor, the modulation may include adjusting the speed of the compressor 106 to a value between a maximum-rated speed and a minimum-rated speed. In embodiments where the compressor 106 is a fixed-speed compressor, the modulation may include cycling the compressor 106 between an activated state and a deactivated state. Modulation of the speed of the compressor 106 impacts the saturated suction temperature such that the saturated suction temperature can be lowered by either deactivating the compressor 106 or reducing a speed of the compressor 106. Following step 308, the process 300 returns to step 304.

FIG. 4 is a graph of time versus discharge air temperature utilizing existing display cases. FIG. 5 is a graph of time versus discharge air temperature utilizing the cooling system 100. As illustrated in FIG. 4, existing display cases exhibit an average saturated suction temperature of 22° F. while, as illustrated in FIG. 5, display cases utilizing the cooling system 100 exhibit a saturated suction temperature of 23° F. While the display case utilizing the cooling system 100 exhibits a higher saturated suction temperature, FIG. 5 illustrates that the display case utilizing the cooling system 100 also exhibits a lower product temperature.

FIG. 6 is a diagram of product temperature utilizing existing cooling systems. FIG. 7 is a diagram of product temperature utilizing the cooling system 100. Referring to FIGS. 6-7 collectively, display case certification determined by, for example, NSF International, requires that an average product temperature not exceed 41° F. and a maximum product temperature not exceed 43° F. FIG. 6 illustrates that existing display cases could exceed NSF standards at many locations within the existing display case. In contrast, FIG. 7 illustrates that display cases utilizing the cooling system 100 exhibit lower product temperatures that are compliant with NSF standards at all locations within the display case.

FIG. 8 is a graph of discharge air temperature versus time comparing existing cooling systems to the cooling system 100. Line 802 illustrates discharge air temperature of an existing cooling system. In region 804, the existing cooling system is defrosted. Line 802 illustrates that, approximately two hours following completion of a defrost cycle, the discharge air temperature begins to rise, which is indicative of frost formation. In comparison, line 806 illustrates discharge air temperature of the cooling system 100. In the region 804, the cooling system 100 is defrosted. Following completion of the defrost cycle, the line 806 illustrates that the discharge air temperature continues to fall, which indicates that frost formation has been delayed.

The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” “generally,” and “about” may be substituted with “within a percentage of” what is specified.

Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

What is claimed is:
 1. A cooling system, comprising: an evaporator coil; a compressor fluidly coupled to the evaporator coil; a circulation fan arranged to direct air through the evaporator coil and through a discharge air duct into a conditioned space; at least one sensor, the at least one sensor being disposed in at least one of the discharge air duct, the conditioned space, and the evaporator coil; an HVAC controller electrically coupled to the at least one sensor and electrically coupled to the compressor; wherein the HVAC controller is configured to: receive a measurement of an HVAC parameter from the at least one sensor; determine if the HVAC parameter indicates frost formation on the evaporator coil; and responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, raise a saturated suction temperature of the evaporator coil.
 2. The cooling system of claim 1, wherein the at east one sensor is a first temperature sensor.
 3. The cooling system of claim 2, wherein the first temperature sensor is disposed at a location that is selected from a group consisting of: in the evaporator coil; and on an exterior surface of the evaporator coil.
 4. The cooling system of claim 3, wherein the HVAC parameter is at least one of: the saturated suction temperature of the evaporator coil; and a surface temperature of the evaporator coil.
 5. The cooling system of claim 1, wherein the at least one sensor is at east one of: a second temperature sensor disposed in the conditioned space; and a flow meter disposed in the discharge air duct.
 6. The cooling system of claim 5, wherein the HVAC parameter is at least one of: a discharge air temperature measured by the second temperature sensor; and a discharge air velocity measured by the flow meter.
 7. The cooling system of claim 1, comprising an evaporator pressure regulator (“EPR”) fluidly coupled between the evaporator coil and the compressor, the EPR being electrically coupled to the HVAC controller.
 8. The cooling system of claim 7, wherein, responsive to the determination that the HVAC parameter indicates frost formation on the evaporator coil, the HVAC controller is configured to signal the EPR to reduce flow of a refrigerant from the evaporator coil to the compressor thereby raising the saturated suction temperature of the evaporator coil.
 9. The cooling system of claim 1, wherein, responsive to the determination that the HVAC parameter indicates frost formation on the evaporator coil, the HVAC controller is configured to signal the compressor to modulate a speed of the compressor thereby raising the saturated suction temperature of the evaporator coil.
 10. The cooling system of claim 9, wherein the HVAC controller is configured to at least one of: reduce the speed of the compressor; and cycle the compressor between an activated state and a deactivated state.
 11. A method for operating a refrigerated display case, the method comprising: measuring, by at least one sensor, an HVAC parameter; determining, by an HVAC controller electrically coupled to the at least one sensor, if the HVAC parameter indicates frost formation on an evaporator coil; and responsive to a determination that the 1-IVAC parameter indicates frost formation on the evaporator coil, signaling, by the HVAC controller, an evaporator pressure regulator (“EPR”) to reduce a flow of refrigerant from an evaporator coil to a compressor thereby raising a saturated suction temperature of the evaporator coil.
 12. The method of claim 11, wherein: the at least one sensor is a first temperature sensor disposed proximate the evaporator coil; and the HVAC parameter is at least one of the saturated suction temperature of the evaporator coil and a surface temperature of the evaporator coil.
 13. The method of claim 11, wherein: the at least one sensor is a second temperature sensor disposed in a conditioned space; and the HVAC parameter is a discharge air temperature.
 14. The method of claim 11, wherein: the at least one sensor is a flow meter; and the HVAC parameter is a discharge air velocity.
 15. A method for operating a refrigerated display case, the method comprising: measuring, by at least one sensor, an HVAC parameter; determining, by an HV AC controller electrically coupled to the at least one sensor, if the HVAC parameter indicates frost formation on an evaporator coil; and responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, signaling, by the HVAC controller, a compressor to modulate a speed of the compressor thereby raising a saturated suction temperature of the evaporator coil.
 16. The method of claim 15, wherein: the at least one sensor is a first temperature sensor disposed proximate the evaporator coil; and the HVAC parameter is at least one of the saturated suction temperature of the evaporator coil and a surface temperature of the evaporator coil.
 17. The method of claim 15, wherein: the at least one sensor is a second temperature sensor disposed in a conditioned space; and the HVAC parameter is a discharge air temperature.
 18. The method of claim 15, wherein: the at least one sensor is a flow meter; and the HVAC parameter is a discharge air velocity.
 19. The method of claim 15, wherein responsive to the signaling the speed of the HVAC controller is reduced.
 70. The method of claim 15, wherein, responsive to the signaling, the compressor is cycled between an activated state and a deactivated state. 